Defenses
 
column spacer Defenses
 
 

Fish defenses

hot buttons for defensive "tasks" for fishes hot button for avoid detection part of the section on fish defenses in the Biology of Caribbean Coral Reefs website hot button for take evasive action part of the section on fish defenses in the Biology of Caribbean Coral Reefs website hot button for prevent capture part of the section on fish defenses in the Biology of Caribbean Coral Reefs website hot button for prevent being eaten if captured part of the section on fish defenses in the Biology of Caribbean Coral Reefs website

Defenses of fishes can be categorised into an heirarchical "cascade" beginning with:

1) avoid detection
2) take evasive action if spotted
3) prevent capture
4) prevent being eaten if captured
5) escape

Of these, the last is obviously the most important, but success in any of the others will aid in achieving it. Note that costs and risks to the prey escalate from first to fourth. The fifth and ultimate category, that of escape, can come at any time and won't be considered further here. The first task of any potential prey fish is to avoid detection.
Helfman et al. 1997 The diversity of fishes. Blackwell Sci Publ.

 
 

Fish defenses: avoid detection: confuse the predator

 

There are many ways for a potential prey fish to avoid detection, but some of the main ones are to confuse the predator, considered in this section, and to HIDE AWAY or to employ CAMOUFLAGE, considered in other sections.

A prey fish can confuse a predator through misdirection or sounds, considered here, or through forming SHOALS & SCHOOLS, considered in another section.

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of a trumpetfish in a gorgonian taken from a video "I guess if hiding away does not stop a predator from finding you, then I guess the next line of strategy is to convince it that what it sees is not what it thinks it sees.." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.
 
 

Fish defenses: avoid detection: confuse the predator: misdirection

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs photograph of a butterflyfish taken from a video

"This foureye butterflyfish has multiple defenses. Eyebars hide the eyes, and the spots at the back may seem to a predator like big eyes...maybe scare it off or cause it to misdirect its attack...and the body is flattened laterally with spines that can be erected. Not bad, huh?." - Turneffe Island, Belize. Video courtesy Andy Stockbridge, Belize.

NOTE Chaetodon capistratus

 
 

photograph of a four-eye butterflyfish Chaetodon capistratus
Many reef fishes have eyebars to disguise the eyes or false eyespots to disdirect attacks by, or otherwise confuse, potential predators.

NOTE eyebars and eyespots are discussed in more detail in FUNCTIONS OF COLOURS: DEFENSE: MIMICRY

 

 

 

 

The eyespot illusion in a foureye butterflyfish
Chaetodon capistratus
is enhanced by a
ring of white around the dark spot and a
partial edging of blue, the latter not
clearly visible in this photograph 1X

 
 

Avoid detection: confuse the predator: sounds

 
 
seahorse dive leader for Biology of Caribbean Coral Reefs website photograph of reef fishes in the Red Sea with unusual sounds taken from a video "Listen to this odd sound. Spooky, huh? Lots of fishes make sounds when disturbed, possibly as a warning to their fellows, or maybe to scare off predators." - Red Sea 2001
 
 

photograph of a shoal of Caesar grunts
Many species of coral-reef fishes emit sounds, most notably distress sounds when confronted or held by a predator. These sounds may act to raise awareness in conspecifics or perhaps attract attention of the predator's own predators.

CLICK on a grunt to hear it grunt. Fish sounds couresy Graduate School of Oceanography, University of Rhode Island. NOTE: if the sounds don't play immediately, you may need to click on the AIFF file that appears at the bottom of this page

 

 

Shoal of Caesar grunts Haemulon carbonarium 0.1X

 
 

photograph of a shoal of Caesar grunts Haemulon carbonarium in the simulated presence of a predatory baraccuda
Grunts and other grunting fishes make their sounds by moving hard body parts against their swim bladders or somehow vibrating their bladders. Other sounds in fishes are created by grinding teeth, rubbing body parts together, or rubbing the bases of spines in their sockets.

To hear louder, more frenzied grunting from the shoal, CLICK on the shoal that is now in the presence of a predator.

 

 

 

The same shoal of grunts, but now with a
predatory barracuda Sphyraena barracuda

 
 

Here are a few more examples. CLICK on each to hear its sounds.

NOTE one of the sounds is actually of the fish feeding...see if you can identify it...answer is at bottom

photograph of a squirrelfish
photograph of a stoplight parrotfish
photograph of a queen triggerfish
  Squirrelfish Holocentrus adscencionis Stoplight parrotfish Sparisoma viride Queen triggerfish Balistes vetula
photograph of ocean surgeonfish
photograph of Nassau grouper
photograph of a dusky damselfish
photograph of queen angelfish
Ocean surgeonfish Acanthurus bahianus Nassau grouper Epinephelus striatus Dusky damselfish Stegastes fuscus

Queen angelfish Holacanthus ciliaris

 
 

So, this is interesting, but what functions are served by these sounds? In addition to confusing or annoying a predator, which is the topic of this section, other possibilities include mate-finding, fright or alarm reaction to a predator, component of migration or navigation, and territorial defense or demarcating territorial boundaries. These last 2 possibilities are the ones most popular with coral-reef scientists.

BITING SOUND: the sound of the queen triggerfish is actually of it feeding on the sea bottom. These triggerfishes eat various types of shellfishes; hence, the crunching sounds. These sounds being made by the stoplight parrotfish may originate from the grinding action of its unique pharyngeal teeth amplified by the adjacent swim bladder. Parrotfishes scrape corals to take in surface algae and embedded symbiotic plant cells, and in so doing make loud and noticeable scraping/crunching sounds.

 
 

photograph of a black margate Anisotremis surinamensis swimming in a school
Schooling black margates Anisotremis surinamensis in Bimini, Bahamas produce 3 sounds, two of which are associated with feeding (burst: a stridulatory sound associated with bottom feeding and pop: associated with feeding in the water column), and one caused by quick swimming and/or positional change of the school (blast).  Bottom foods are mostly shellfishes (worms, stomatopods, shrimps, and crabs); planktonic foods, mostly larval and juvenile fishes.  Margates in this area are preyed upon mostly by barricudas Sphyraena barracuda and amberjacks Seriola dumerili.  In response to approach by a predator, the margates school more closely at the sea bottom and emit blast sounds.  A fourth sound, a grating one, is commonly emitted by hand-held margates, but the authors remark that in 5yr of bio-acoustic studies in the Bahamas this sound was never recorded. 
Cummings et al. 1966 Bull Mar Sci 16 (3): 627.

NOTE  the authors do not try to explain what these noises actually sound like

Black margate Anisotremus surinamensis swimming in a school 0.3X
 
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hot area to hear a grunt making a sound hot area to hear a shoal of grunts making frenzied sounds hot area to hear grunts making frenzied scared sounds hot area to hear squirrelfish making sounds hot area to hear stoplight parrotfish making noises hot area to hear queen triggerfish making noises hot area to hear ocean surgeonfish making noises hot area to hear Nassau grouper making noises hot area to hear dusky damselfish making noises hot area to hear queen angelfish making noises